One document matched: draft-ietf-netconf-yang-push-03.xml
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<front>
<title abbrev="YANG-Push">Subscribing to YANG datastore push
updates</title>
<author fullname="Alexander Clemm" initials="A." surname="Clemm">
<organization>Cisco Systems</organization>
<address>
<email>alex@cisco.com</email>
</address>
</author>
<author fullname="Alberto Gonzalez Prieto" initials="A."
surname="Gonzalez Prieto">
<organization>Cisco Systems</organization>
<address>
<email>albertgo@cisco.com</email>
</address>
</author>
<author fullname="Eric Voit" initials="E." surname="Voit">
<organization>Cisco Systems</organization>
<address>
<email>evoit@cisco.com</email>
</address>
</author>
<author fullname="Ambika Prasad Tripathy" initials="A." surname="Tripathy">
<organization>Cisco Systems</organization>
<address>
<email>ambtripa@cisco.com</email>
</address>
</author>
<author fullname="Einar Nilsen-Nygaard" initials="E."
surname="Nilsen-Nygaard">
<organization>Cisco Systems</organization>
<address>
<email>einarnn@cisco.com</email>
</address>
</author>
<date day="15" month="June" year="2016"/>
<abstract>
<t>This document defines a subscription and push mechanism for YANG
datastores. This mechanism allows client applications to request updates
from a YANG datastore, which are then pushed by the server to a receiver
per a subscription policy, without requiring additional client
requests.</t>
</abstract>
</front>
<middle>
<section title="Introduction">
<t>YANG <xref target="RFC6020"/> was originally designed for the Netconf
protocol <xref target="RFC6241"/>, which originally put most emphasis on
configuration. However, YANG is not restricted to configuration data.
YANG datastores, i.e. datastores that contain data modeled according
using YANG, can contain configuration as well as operational data. It is
therefore reasonable to expect that data in YANG datastores will
increasingly be used to support applications that are not focused on
managing configurations but that are, for example, related to service
assurance.</t>
<t>Service assurance applications typically involve monitoring
operational state of networks and devices; of particular interest are
changes that this data undergoes over time. Likewise, there are
applications in which data and objects from one datastore need to be
made available both to applications in other systems and to remote
datastores <xref target="I-D.voit-netmod-yang-mount-requirements"/>
<xref target="I-D.clemm-netmod-mount"/>. This requires mechanisms that
allow remote systems to become quickly aware of any updates to allow to
validate and maintain cross-network integrity and consistency.</t>
<t>Traditional approaches to remote network state visibility rely
heavily on polling. With polling, data is periodically explicitly
retrieved by a client from a server to stay up-to-date.</t>
<t>There are various issues associated with polling-based management:
<list style="symbols">
<t>It introduces additional load on network, devices, and
applications. Each polling cycle requires a separate yet arguably
redundant request that results in an interrupt, requires parsing,
consumes bandwidth.</t>
<t>It lacks robustness. Polling cycles may be missed, requests may
be delayed or get lost, often particularly in cases when the network
is under stress and hence exactly when the need for the data is the
greatest.</t>
<t>Data may be difficult to calibrate and compare. Polling requests
may undergo slight fluctuations, resulting in intervals of different
lengths which makes data hard to compare. Likewise, pollers may have
difficulty issuing requests that reach all devices at the same time,
resulting in offset polling intervals which again make data hard to
compare.</t>
</list> A more effective alternative is when an application can
request to be automatically updated as necessary of current content of
the datastore (such as a subtree, or data in a subtree that meets a
certain filter condition), and in which the server that maintains the
datastore subsequently pushes those updates. However, such a solution
does not currently exist.</t>
<t>The need to perform polling-based management is typically considered
an important shortcoming of management applications that rely on MIBs
polled using SNMP <xref target="RFC1157"/>. However, without a provision
to support a push-based alternative, there is no reason to believe that
management applications that operate on YANG datastores using protocols
such as NETCONF or Restconf <xref target="I-D.ietf-netconf-restconf"/>
will be any more effective, as they would follow the same
request/response pattern.</t>
<t>While YANG allows the definition of notifications, such notifications
are generally intended to indicate the occurrence of certain
well-specified event conditions, such as a the onset of an alarm
condition or the occurrence of an error. A capability to subscribe to
and deliver event notifications has been defined in <xref
target="RFC5277"/>. In addition, configuration change notifications have
been defined in <xref target="RFC6470"/>. These change notifications
pertain only to configuration information, not to operational state, and
convey the root of the subtree to which changes were applied along with
the edits, but not the modified data nodes and their values.
Furthermore, while delivery of updates using notifications is a viable
option, some applications desire the ability to stream updates using
other transports. </t>
<t>Accordingly, there is a need for a service that allows client
applications to dynamically subscribe to updates of a YANG datastore and
that allows the server to push those updates, possibly using one of
several delivery mechanisms. Additionally, support for
subscriptions configured directly on the server are also useful
when dynamic signaling is undesirable or unsupported. The requirements
for such a service are documented in <xref
target="I-D.i2rs-pub-sub-requirements"/>.
</t>
<t>This document proposes a
solution. The solution builds on top of the Netconf Event Model
<xref target="I-D.gonzalez-netconf-5277bis"/> which defines a
mechanism for the management of event subscriptions. At its core,
the solution
that is defined here introduces a new set of event streams including
datastore push updates that clients can subscribe to, as well as
extensions to the event subscription model that allow to manage policies
that define what and when updates are trigged. To this end,
the document specifies a YANG data model that augments the
YANG data model (and RPCs) defined as part of the NETCONF Event Model.
</t>
<t>Specifically, the solution
features the following capabilities: <list style="symbols">
<t>An extension to event subscription mechanisms allows clients to
subscribe to event streams containing
automatic datastore updates. The subscription allows clients to
specify which data
they are interested in, what types of updates (e.g. create, delete,
modify), and to provide optional filters with
criteria that data must meet for updates to be sent. Furthermore,
subscriptions can specify a policy that directs when updates are
provided. For example, a client may request to be updated
periodically in certain intervals, or whenever data changes
occur. </t>
<t>The ability for a server to push back on requested subscription
parameters. Because not every server may support every requested
update policy for every piece of data, it is necessary for a server to be
able to indicate whether or not it is capable of supporting a
requested subscription, and possibly allow to negotiate push update
subscription parameters. For example, some servers may have a
lower limit to the period with which they can send updates, or they
may not support on-change updates for every piece of data. </t>
<t>A mechanism to communicate the updates themselves. For this, the
proposal leverages and extends existing YANG/Netconf/Restconf
mechanisms, defining special notifications that carry updates.
In addition, optional subscription parameters allow to specify which
transport should be used to stream updates, and to define QoS
extensions that allow to address aspects such as how to
prioritize between streams of updates. </t>
</list>
</t>
</section>
<section title="Definitions and Acronyms">
<t>Data node: An instance of management information in a YANG
datastore.</t>
<t>Data record: A record containing a set of one or more data node
instances and their associated values.</t>
<t>Datastore: A conceptual store of instantiated management information,
with individual data items represented by data nodes which are arranged
in hierarchical manner.</t>
<t>Datastream: A continuous stream of data records, each including a set
of updates, i.e. data node instances and their associated values.</t>
<t>Data subtree: An instantiated data node and the data nodes that are
hierarchically contained within it.</t>
<t>Dynamic subscription: A subscription negotiated between subscriber
and publisher vian establish, modify, and delete RPCs respectively
control plane signaling messages that are part of an existing management
association between and publisher. Subscriber and receiver are the same
system.</t>
<t>NACM: NETCONF Access Control Model</t>
<t>NETCONF: Network Configuration Protocol</t>
<t>Publisher: A server that sends push updates to a receiver according
to the terms of a subscription. In general, the publisher is also the
"owner" of the subscription.</t>
<t>Push-update stream: A conceptual data stream of a datastore that
streams the entire datastore contents continuously and perpetually.</t>
<t>Receiver: The target of push updates of a subscription. In case of a
dynamic subscription, receiver and subscriber are the same system.
However, in the case of a configured subscription, the receiver may be a
different system than the one that configured the subscription.</t>
<t>RPC: Remote Procedure Call</t>
<t>SNMP: Simple Network Management Protocol</t>
<t>Configured subscription: A subscription installed as part of a
configuration datastore via a configuration interface.</t>
<t>Subscriber: A client that negotiates a subscription with a server
("publisher"). A client that establishes a configured subscription is also
considered a subscriber, even if it is not necessarily the receiver of a
subscription.</t>
<t>Subscription: A contract between a client ("subscriber") and a server
("publisher"), stipulating which information the client wishes to
receive from the server (and which information the server has to provide
to the client) without the need for further solicitation.</t>
<t>Subscription filter: A filter that contains evaluation criteria which
are evaluated against YANG objects of a subscription. An update is only
published if the object meets the specified filter criteria.</t>
<t>Subscription policy: A policy that specifies under what circumstances
to push an update, e.g. whether updates are to be provided periodically
or only whenever changes occur.</t>
<t>Update: A data item containing the current value of a data node.</t>
<t>Update trigger: A trigger, as specified by a subscription policy,
that causes an update to be sent, respectively a data record to be
generated. An example of a trigger is a change trigger, invoked when the
value of a data node changes or a data node is created or deleted, or a
time trigger, invoked after the laps of a periodic time interval.</t>
<t>URI: Uniform Resource Identifier</t>
<t>YANG: A data definition language for NETCONF</t>
<t>YANG-Push: The subscription and push mechanism for YANG datastores
that is specified in this document.</t>
</section>
<section title="Solution Overview">
<t>This document specifies a solution for a push update subscription
service, which
supports the dynamic as well as static (via configuration) creation of
subscriptions to
information updates of operational or configuration YANG data which are
subsequently pushed from the server to the client.</t>
<t>Dynamic subscriptions are initiated by clients who want to receive
push updates. Servers respond to requests for the creation of
subscriptions positively or negatively. Negative responses MAY include
information about why the subscription was not accepted, in order to
facilitate converging on an acceptable set of subscription parameters.
Similarly, configured subscriptions are configured as part of a device's
configuration. Once a subscription has been established, datastore push
updates are pushed from the server to the receiver until the
subscription ends.</t>
<t>Accordingly, the solution encompasses several components: <list
style="symbols">
<t>The subscription model for configuration and management of the
subscriptions.</t>
<t>The ability to provide hints for acceptable subscription
parameters, in cases where a subscription desired by a client cannot
currently be served.</t>
<t>The stream of push updates.</t>
</list> In addition, there are a number of additional considerations,
such as the tie-in of the mechanisms with security mechanisms. Each of
those aspects will be discussed in the following subsections.</t>
<section title="Subscription Model">
<t>YANG-Push subscriptions are defined using a data model that is
itself defined in YANG. This model augments the
event subscription model
defined in <xref target="I-D.gonzalez-netconf-5277bis"/>
and introduces several new parameters, for example parameters
that allow subscribers to specify what to include in an update,
what triggers an update, and how to deliver updates.
</t>
<t>The subscription model assumes the presence of one or more conceptual
perpetual datastreams of continuous updates
that can be subscribed to. There are several datastreams with predefined
semantics,
such as the stream of updates of all operational data or the stream
of updates of all config data. In addition, it is possible to define
custom streams with customizable semantics.
The model includes the list of update datastreams that are supported
by a system and available for subscription.
</t>
<t>
The subscription model augments the NETCONF event subscription
model with a set of parameters as follows: <list style="symbols">
<t>An encoding for push updates. By default, updates are
encoded using XML, but JSON can be requested as an option and
other encodings may be supported in the future.</t>
<t>An optional start time for the subscription. If the specified
start time is in the past, the subscription goes into effect
immediately. The start time also serves as anchor time for
periodic subscriptions, from which intervals at which to send
updates are calculated (see also below).</t>
<t>An optional stop time for the subscription. Once the stop time
is reached, the subscription is automatically terminated.</t>
<t>A subscription policy definition regarding the update trigger
when to send new updates. The trigger can be periodic or based on
change. <list style="symbols">
<t>For periodic subscriptions, the trigger is defined by a
parameter that defines the interval with which updates are to
be pushed. The start time of the subscription serves as anchor
time, defining one specific point in time at which an update
needs to be sent. Update intervals always fall on the points
in time that are a multiple of a period after the start
time.
</t>
<t>EDITOR'S NOTE: A possible option to discuss concerns
the introduction of an additional
parameter "changes-only" for periodic subscription.
Including this flag would results in sending
at the end of each period an
update containing only changes since the last update
(i.e. a change-update as in the case of an on-change subscription),
not a full snapshot of the subscribed information. Such an
option might be interesting in case of data that is largely static
and bandwidth-constrained environments.
</t>
<t>For on-change subscriptions, the trigger occurs whenever a
change in the subscribed information is detected. On-change
subscriptions have more complex semantics that can be guided
by additional parameters. Please refer also to <xref
target="on-change"/>. <list style="symbols">
<t>One parameter specifies the dampening
period, i.e. the interval that must pass before a
successive update for the same data node is sent. The
first time a change is detected, the update is sent
immediately. If a subsequent change is detected, another
update for that object is only sent once the dampening
period has passed,
containing the value of the data node that is then
valid. Note that the dampening period applies to each object,
not the set of all objects that are part of the
same subscription. This means that on the first change of
an object, an update for that object is immediately sent,
regardless of whether or not for another object of the same
subscription a dampening period is already in effect. </t>
<t>Another parameter allows to restrict the types of
changes for which updates are sent (changes to object
values, object creation or deletion events). It is
conceivable to augment the data model with additional
parameters in the future to specify even more refined
policies, such as parameters that specify the magnitude of
a change that must occur before an update is
triggered.</t>
<t>A third parameter specifies whether or not a complete
update with all the subscribed data should be sent at the
beginning of a subscription to facilitate synchronization
and establish the frame of reference for subsequent
updates.</t>
<t>EDITOR'S NOTE: Several semantic variations
are conceivable. In one variation, an on-change notification
is sent immediately, but successive dampening
updates are sent at fixed period intervals, grouping all changes
of objects for which changes have occurred since the sending
of their last update and the current dampening period.
</t>
</list></t>
</list></t>
<t>Optionally, a filter, or set of filters, describing the subset
of data items in the stream's data records that are of interest to
the subscriber. The server should only send to the subscriber the
data items that match the filter(s), when present. The absence of
a filter indicates that all data items from the stream are of
interest to the subscriber and all data records must be sent in
their entirety to the subscriber. The following types of filters are
introduced: subtree filters, with the same semantics as defined in
[RFC 6241],and XPath filters. In addition, as with any subscription,
an RFC 5277 filter MAY be used, with the same
semantics as defined in [RFC 5277]. Additional filter types can be
added through augmentations. Filters can be specified "inline" as
part of the subscription, or can be configured separately and
referenced by a subscription, in order to facilitate reuse of
complex filters.</t>
</list></t>
<t>The subscription data model is specified as part of the YANG data
model described later in this specification. Specifically, the
subscription parameters are defined in the "subscription-info" and
"update-policy" groupings. Receiver information is defined in the
"receiver-info" grouping. Information about the source address is
defined in the "push-source-info" grouping. It is conceivable that
additional subscription parameters might be added in the future. This
can be accomplished through augmentation of the subscription data
model.</t>
</section>
<section title="Negotiation of Subscription Policies">
<t>A subscription rejection can be caused by the inability of the
server to provide a stream with the requested semantics. For example,
a server may not be able to support "on-change" updates for
operational data, or only support them for a limited set of data
nodes. Likewise, a server may not be able to support a requested
update frequency.</t>
<t>YANG-Push supports a simple negotiation between clients and servers
for subscription parameters. The negotiation is limited to a single
pair of subscription request and response. For negative responses, the
server SHOULD include in the returned error what subscription
parameters would have been accepted for the request. The returned
acceptable parameters constitute suggestions that, when followed,
increase the likelihood of success for subsequent requests. However,
they are no guarantee that subsequent requests for this client or
others will in fact be accepted.</t>
<t>In case a subscriber requests an encoding other than XML, and this
encoding is not supported by the server, the server simply indicates
in the response that the encoding is not supported.</t>
<t>A subscription negotiation capability has been introduced as part
of the NETCON Event Notifications model. However, the ability to
negotiate subscriptions is of particular importance in conjunction
with push updates, as server implementations may have limitations
with regards to
what updates can be generated and at what velocity.
</t>
</section>
<section anchor="on-change" title="On-Change Considerations">
<t>On-change subscriptions allow clients to subscribe to updates
whenever changes to objects occur. As such, on-change subscriptions
are of particular interest for data that changes relatively
infrequently, yet that require applications to be notified with
minimal delay when changes do occur.</t>
<t>On-change subscriptions tend to be more difficult to implement than
periodic subscriptions. Specifically, on-change subscriptions may
involve a notion of state to see if a change occurred between past and
current state, or the ability to tap into changes as they occur in the
underlying system. Accordingly, on-change subscriptions may not be
supported by all implementations or for every object.</t>
<t>When an on-change subscription is requested for a datastream with a
given subtree filter, where not all objects support on-change update
triggers, the subscription request MUST be rejected. As a result,
on-change subscription requests will tend to be directed at very
specific, targeted subtrees with only few objects.</t>
<t>Any updates for an on-change subscription will include only objects
for which a change was detected. To avoid flooding clients with
repeated updates for fast-changing objects, or objects with
oscillating values, an on-change subscription allows for the
definition of a dampening period. Once an update for a given object is
sent, no other updates for this particular object are sent until the
end of the dampening period. Values sent at the end of the dampening
period are the values current when that dampening period expires. In
addition, updates include information about objects that were deleted
and ones that were newly created.</t>
<t>On-change subscriptions can be refined to let users subscribe only
to certain types of changes, for example, only to object creations and
deletions, but not to modifications of object values.</t>
<t>Additional refinements are conceivable. For example, in order to
avoid sending updates on objects whose values undergo only a
negligible change, additional parameters might be added to an
on-change subscription specifying a policy that states how large or
"significant" a change has to be before an update is sent. A simple
policy is a "delta-policy" that states, for integer-valued data nodes,
the minimum difference between the current value and the value that
was last reported that triggers an update. Also more sophisticated
policies are conceivable, such as policies specified in percentage
terms or policies that take into account the rate of change. While not
specified as part of this draft, such policies can be accommodated by
augmenting the subscription data model accordingly.</t>
</section>
<section title="Data Encodings">
<t>Subscribed data is encoded in either XML or JSON format. A server
MUST support XML encoding and MAY support JSON encoding.</t>
<t>It is conceivable that additional encodings may be supported as
options in the future. This can be accomplished by augmenting the
subscription data model with additional identity statements used to
refer to requested encodings.</t>
<section title="Periodic Subscriptions">
<t>In a periodic subscription, the data included as part of an
update corresponds to data that could have been simply retrieved
using a get operation and is encoded in the same way. XML encoding
rules for data nodes are defined in <xref target="RFC6020"/>. JSON
encoding rules are defined in <xref
target="I-D.ietf-netmod-yang-json"/>. This encoding is valid JSON,
but also has special encoding rules to identify module namespaces
and provide consistent type processing of YANG data.</t>
</section>
<section title="On-Change Subscriptions">
<t>In an on-change subscription, updates need to allow to
differentiate between data nodes that were newly created since the
last update, data nodes that were deleted, and data nodes whose
value changed.</t>
<t>XML encoding rules correspond to how data would be encoded in
input to Netconf edit-config operations as specified in <xref
target="RFC6241"/> section 7.2, adding "operation" attributes to
elements in the data subtree. Specifically, the following values
will be utilized: <list style="symbols">
<t>create: The data identified by the element has been added
since the last update.</t>
<t>delete: The data identified by the element has been deleted
since the last update.</t>
<t>merge: The data identified by the element has been changed
since the last update.</t>
<t>replace: The data identified by the element has been replaced
with the update contents since the last update.</t>
</list> The remove value will not be utilized.</t>
<t>Contrary to edit-config operations, the data is sent from the
server to the client, not from the client to the server, and will
not be restricted to configuration data.</t>
<t>JSON encoding rules are roughly analogous to how data would be
encoded in input to a YANG-patch operation, as specified in <xref
target="I-D.ietf-netconf-yang-patch"/> section 2.2. However, no
edit-ids will be needed. Specifically, changes will be grouped under
respective "operation" containers for creations, deletions, and
modifications.</t>
</section>
</section>
<section title="Subscription Filters">
<t>Subscriptions can specify filters for subscribed data. The
following filters are supported in addition to RFC 5277 filters that
apply to any event subscription:
<list style="symbols">
<t>subtree-filter: A subtree filter specifies a subtree that the
subscription refers to. When specified, updates will only concern
data nodes from this subtree. Syntax and semantics correspond to
that specified for <xref target="RFC6241"/> section 6.</t>
<t>xpath-filter: An XPath filter specifies an XPath expression
applied to the data in an update, assuming XML-encoded data.</t>
</list> Only a single filter can be applied to a subscription at a
time.</t>
<t>It is conceivable for implementations to support other filters. For
example, an on-change filter might specify that changes in values
should be sent only when the magnitude of the change since previous
updates exceeds a certain threshold. It is possible to augment the
subscription data model with additional filter types.</t>
</section>
<section title="Push Data Stream and Transport Mapping">
<t>Pushing data based on a subscription could be considered analogous
to a response to a data retrieval request, e.g. a "get" request.
However, contrary to such a request, multiple responses to the same
request may get sent over a longer period of time.</t>
<t>A more suitable mechanism to consider is therefore that of a
notification. There are however some specifics that need to be
considered. Contrary to other notifications that are associated with
alarms and unexpected event occurrences, push updates are solicited,
i.e. tied to a particular subscription which triggered the
notification, and arguably only of interest to the subscriber,
respectively the intended receiver of the subscription. A subscription
therefore needs to be able to distinguish between streams that
underlie push updates and streams of other notifications. By the same
token, notifications associated with updates and subscriptions to
updates need to be distinguished from other notifications, in that
they enter a datastream of push updates, not a stream of other event
notifications.</t>
<t>A push update notification contains several parameters: <list
style="symbols">
<t>A subscription correlator, referencing the name of the
subscription on whose behalf the notification is sent.</t>
<t>A data node that contains a representation of the datastore
subtree containing the updates. The subtree is filtered per access
control rules to contain only data that the subscriber is
authorized to see. Also, depending on the subscription type, i.e.,
specifically for on-change subscriptions, the subtree contains
only the data nodes that contain actual changes. (This can be
simply a node of type string or, for XML-based encoding,
anyxml.)</t>
</list> Notifications are sent using <notification> elements
as defined in <xref target="RFC5277"/>. Alternative transports are
conceivable but outside the scope of this specification.</t>
<t>The solution specified in this document uses notifications to
define datastore updates. The contents of the notification includes a
set of explicitly defined data nodes. For this purpose, two new
generic notifications are introduced, "push-update" and
"push-change-update". Those notifications define how mechanisms that
carry YANG notifications (e.g. Netconf notifications and Restconf) can
be used to carry data records with updates of datastore contents as
specified by a subscription. It is possible also map notifications to
other transports and encodings and use the same subscription model;
however, the definition of such mappings is outside the scope of this
document.</t>
<t>Push-update notification defines updates for a periodic
subscription, as well as for the initial update of an on-change
subscription used to synchronize the receiver at the start of a new
subscription. The update record contains a data snippet that contains
an instantiated subtree with the subscribed contents. The content of
the update record is equivalent to the contents that would be obtained
had the same data been explicitly retrieved using e.g. a Netconf
"get"-operation, with the same filters applied.</t>
<t>The contents of the notification conceptually represents the union
of all data nodes in the yang modules supported by the server.
However, in a YANG data model, it is not practical to model the
precise data contained in the updates as part of the notification.
This is because the specific data nodes supported depend on the
implementing system and may even vary dynamically. Therefore, to
capture this data, a single parameter that can represent any datastore
contents is used, not parameters that represent data nodes one at a
time.</t>
<t>Push-change-update notification defines updates for on-change
subscriptions. The update record here contains a data snippet that
indicates the changes that data nodes have undergone, i.e. that
indicates which data nodes have been created, deleted, or had changes
to their values. The format follows the same format that operations
that apply changes to a data tree would apply, indicating the creates,
deletes, and modifications of data nodes.</t>
<t>The following is an example of push notification. It contains an
update for subscription 1011, including a subtree with root foo that
contains a leaf, bar:</t>
<figure align="center" anchor="push-example" title="Push example">
<artwork align="left"><![CDATA[
<notification
xmlns="urn:ietf:params:xml:ns:netconf:notification:1.0">
<eventTime>2015-03-09T19:14:56Z</eventTime>
<push-update
xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-push:1.0">
<subscription-id>1011</subscription-id>
<time-of-update>2015-03-09T19:14:56Z</time-of-update>
<datastore-contents-xml>
<foo>
<bar>some_string</bar>
</foo>
</datastore-contents-xml>
</push-update>
</notification>
]]></artwork>
</figure>
<t>The following is an example of an on-change notification. It
contains an update for subscription 89, including a new value for a
leaf called beta, which is a child of a top-level container called
alpha:</t>
<figure align="center" anchor="push-example-on-change"
title="Push example for on change">
<artwork align="left"><![CDATA[
<notification
xmlns="urn:ietf:params:xml:ns:netconf:notification:1.0">
<eventTime>2015-03-09T19:14:56Z</eventTime>
<push-change-update xmlns=
"urn:ietf:params:xml:ns:yang:ietf-yang-push:1.0">
<subscription-id>89</subscription-id>
<time-of-update>2015-03-09T19:14:56Z</time-of-update>
<datastore-changes-xml>
<alpha xmlns="http://example.com/sample-data/1.0" >
<beta>1500</beta>
</alpha>
</datastore-changes-xml>
</push-change-update>
</notification>
]]></artwork>
</figure>
<t>The equivalent update when requesting json encoding:</t>
<figure align="center" anchor="push-example-on-change-json"
title="Push example for on change with JSON">
<artwork align="left"><![CDATA[
<notification
xmlns="urn:ietf:params:xml:ns:netconf:notification:1.0">
<eventTime>2015-03-09T19:14:56Z</eventTime>
<push-change-update xmlns=
"urn:ietf:params:xml:ns:yang:ietf-yang-push:1.0">
<subscription-id>89</subscription-id>
<time-of-update>2015-03-09T19:14:56Z</time-of-update>
<datastore-changes-json>
{
"ietf-yang-patch:yang-patch": {
"patch-id": [
null
],
"edit": [
{
"edit-id": "edit1",
"operation": "merge",
"target": "/alpha/beta",
"value": {
"beta": 1500
}
}
]
}
}
</datastore-changes-json>
</push-change-update>
</notification>
]]></artwork>
</figure>
<t>When the beta leaf is deleted, the server may send</t>
<figure align="center" anchor="push-example-on-change-2"
title="2nd push example for on change update">
<artwork align="left"><![CDATA[
<notification
xmlns="urn:ietf:params:xml:ns:netconf:notification:1.0">
<eventTime>2015-03-09T19:14:56Z</eventTime>
<push-change-update xmlns=
"urn:ietf:params:xml:ns:yang:ietf-yang-push:1.0">
<subscription-id>89</subscription-id>
<time-of-update>2015-03-09T19:14:56Z</time-of-update>
<datastore-changes-xml>
<alpha xmlns="http://example.com/sample-data/1.0" >
<beta urn:ietf:params:xml:ns:netconf:base:1.0:
operation="delete"/>
</alpha>
</datastore-changes-xml>
</push-change-update>
</notification>
]]></artwork>
</figure>
</section>
<section title="Subscription management">
<t>There are two ways in which subscriptions can be managed, as specified
in the NETCONF Event Notifications model: RPC-based
and configuration based. Any given subscription is either RPC-based or
configuration-based. There is no mixing-and-matching of RPC and
configuration operations. Specifically, a configured subscription
cannot be modified or deleted using RPC. Likewise, a subscription
established via RPC cannot be modified or deleted through
configuration operations.</t>
<t>The following sections describe how subscription management is
applied to YANG Push subscriptions.
</t>
<section title="Subscription management by RPC">
<t>RPC-based subscription allows a subscriber to establish a
subscription via an RPC call. The subscriber and the receiver are
the same entity, i.e. a subscriber cannot subscribe or in other ways
interfere with a subscription on another receiver's behalf. The
lifecycle of the subscription is dependent on the lifecyle of the
transport session over which the subscription was requested. For
example, when a Netconf session over which a subscription was
established is torn down, the subscription is automatically
terminated (and needs to be re-initiated when a new session is
established). Alternatively, a subscriber can also decide to delete
a subscription via another RPC.</t>
<t>When an establish-subscription request is successful, the
subscription identifier of the freshly established subscription is
returned.</t>
<t>A subscription can be rejected for multiple reasons, including
the lack of authorization to establish a subscription, the lack of
read authorization on the requested data node, or the inability of
the server to provide a stream with the requested semantics. In such
cases, no subscription is established. Instead, the
subscription-result with the failure reason is returned as part of
the RPC response. In addition, a set of alternative subscription
parameters MAY be returned that would likely have resulted in
acceptance of the subscription request, which the subscriber may try
for a future subscription attempt.</t>
<t>It should be noted that a rejected subscription does not result
in the generation of an rpc-reply with an rpc-error element, as
neither the specification of YANG-push specific errors nor the
specification of additional data parameters to be returned in an
error case are supported as part of a YANG data model.</t>
<t>For instance, for the following request:</t>
<figure align="center" anchor="establish-subscription"
title="Establish-Subscription example">
<artwork align="left"><![CDATA[
<netconf:rpc message-id="101"
xmlns:netconf="urn:ietf:params:xml:ns:netconf:base:1.0">
<establish-subscription
xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-push:1.0">
<stream>push-update</stream>
<filter netconf:type="xpath"
xmlns:ex="http://example.com/sample-data/1.0"
select="/ex:foo"/>
<period>500</period>
<encoding>encode-xml</encoding>
</establish-subscription>
</netconf:rpc>
]]></artwork>
</figure>
<t>the server might return:</t>
<figure align="center"
anchor="establish-subscription-error-response"
title="Error response example">
<artwork align="left"><![CDATA[
<rpc-reply message-id="101"
xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
<subscription-result
xmlns="http://urn:ietf:params:xml:ns:yang:ietf-yang-push:1.0">
error-insufficient-resources
</subscription-result>
<period>2000</period>
</rpc-reply>
]]></artwork>
</figure>
<t>A subscriber that establishes a subscription using RPC can modify
or delete the subscription using other RPCs. When the session
between subscriber and publisher is terminated, the subscription is
implicitly deleted.</t>
</section>
<section title="Subscription management by configuration">
<t>Configuration-based subscription allows a subscription to be
established as part of a server's configuration. This allows to
persist subscriptions. Persisted subscriptions allow for a number of
additional options than RPC-based subscriptions. As part of a
configured subscription, a receiver needs to be specified. It is
thus possible to have a different system acting as subscriber (the
client creating the subscription) and as receiver (the client
receiving the updates). In addition, a configured subscription
allows to specify which transport protocol should be used, as well
as the sender source (for example, a particular interface or an
address of a specific VRF) from which updates are to be pushed.</t>
<t>Configuration-based subscriptions cannot be modified or deleted
using RPCs. Instead, configured subscriptions are deleted as part of
regular configuration operations. Servers SHOULD reject attempts to
modify configurations of active subscriptions. This way, race
conditions in which a receiver may not be aware of changed
subscription policies are avoided.</t>
</section>
</section>
<section title="Other considerations">
<section anchor="Authorization" title="Authorization">
<t>A receiver of subscription data may only be sent updates for
which they have proper authorization. Data that is being pushed
therefore needs to be subjected to a filter that applies all
corresponding rules applicable at the time of a specific pushed
update, removing any non-authorized data as applicable.</t>
<t>The authorization model for data in YANG datastores is described
in the Netconf Access Control Model <xref target="RFC6536"/>.
However, some clarifications to that RFC are needed so that the
desired access control behavior is applied to pushed updates.</t>
<t>One of these clarifications is that a subscription may only be
established if the Receiver has read access to the target data
node.</t>
<figure align="center" anchor="access-control-subscription"
title="Access control for subscription">
<artwork align="left"><![CDATA[
+-------------+ +-------------+
subscription | protocol | | target |
request --> | operation | -------------> | data node |
| allowed? | datastore | access |
+-------------+ or state | allowed? |
data access +-------------+
]]></artwork>
</figure>
<t>Likewise if a receiver no longer has read access permission to a
target data node, the subscription must be abnormally terminated
(with loss of access permission as the reason provided).</t>
<t>Another clarification to <xref target="RFC6536"/> is that each of
the individual nodes in a pushed update must also go through access
control filtering. This includes new nodes added since the last push
update, as well as existing nodes. For each of these read access
must be verified. The methods of doing this efficiently are left to
implementation.</t>
<figure align="center" anchor="access-control-push-update"
title="Access control for push updates">
<artwork align="left"><![CDATA[
+-------------+ +-------------------+
subscription | data node | yes | |
update --> | access | ---> | add data node |
| allowed? | | to update message |
+-------------+ +-------------------+
]]></artwork>
</figure>
<t>If there are read access control changes applied under the target
node, no notifications indicating the fact that this has occurred
need to be provided.</t>
</section>
<section title="Additional subscription primitives">
<t>Other possible operations include the ability for a Subscriber to
request the suspension/resumption of a Subscription with a
Publisher. However, subscriber driven suspension is not viewed as
essential at this time, as a simpler alternative is to remove a
subscription and reestablish it when needed.</t>
<t>It should be noted that this does not affect the ability of the
Publisher to suspend a subscription. This can occur in cases the
server is not able to serve the subscription for a certain period of
time, and indicated by a corresponding notification.</t>
</section>
<section title="Robustness and reliability considerations">
<t>Particularly in the case of on-change push updates, it is
important that push updates do not get lost.</t>
<t>YANG-Push uses a secure and reliable transport. Notifications are
not getting reordered, and in addition contain a time stamp. For
those reasons, for the transport of push-updates, we believe that
additional reliability mechanisms at the application level, such as
sequence numbers for push updates, are not required.</t>
<t>At the same time, it is conceivable that under certain
circumstances, a push server is not able to generate the update
notifications that it had committed to when accepting a subcription.
In those circumstances, the server needs to inform the receiver of
the situation. For this purpose, notifications are defined that a
push server can use to inform subscribers/ receivers when a
subscription is (temporarily) suspended, when a suspended
subscription is resumed, and when a a subscription is terminated.
This way, receivers will be able to rely on a subscription, knowing
that they will be informed of any situations in which updates might
be missed.</t>
</section>
<section title="Update size and fragmentation considerations">
<t>Depending on the subscription, the volume of updates can become
quite large. There is no inherent limitation to the amount of data
that can be included in a notification. That said, it may not always
be practical to send the entire update in a single chunk.
Implementations MAY therefore choose, at their discretion, to
"chunk" updates and break them out into several update
notifications.</t>
</section>
<section title="Push data streams">
<t>There are several conceptual data streams introduced in this
specification: <list style="symbols">
<t>yang-push includes the entirety of YANG data, including both
configuration and operational data.</t>
<t>operational-push includes all operational (read-only) YANG
data</t>
<t>config-push includes all YANG configuration data.</t>
</list> It is conceivable to introduce other data streams with
more limited scope, for example: <list style="symbols">
<t>operdata-nocounts-push, a datastream containing all
operational (read-only) data with the exception of counters</t>
<t>other custom datastreams</t>
</list></t>
<t>Those data streams make particular sense for use cases involving
service assurance (not relying on operational data), and for use
cases requiring on-change update triggers which make no sense to
support in conjunction with fast-changing counters. While it is
possible to specify subtree filters on yang-push to the same effect,
having those data streams greatly simplifies articulating
subscriptions in such scenarios.</t>
</section>
<section anchor="implementation-considerations"
title="Implementation considerations">
<t>Implementation specifics are outside the scope of this
specification. That said,it should be noted that monitoring of
operational state changes inside a system can be associated with
significant implementation challenges.</t>
<t>Even periodic retrieval of operational state alone, to be able to
push it, can consume considerable system resources. Configuration
data may in many cases be persisted in an actual database or a
configuration file, where retrieval of the database content or the
file itself is reasonably straightforward and computationally
inexpensive. However, retrieval of operational data may, depending
on the implementation, require invocation of APIs, possibly on an
object-by-object basis, possibly involving additional internal
interrupts, etc.</t>
<t>For those reasons, if is important for an implementation to
understand what subscriptions it can or cannot support. It is far
preferrable to decline a subscription request, than to accept it
only to result in subsequent failure later.</t>
<t>Whether or not a subscription can be supported will in general be
determined by a combination of several factors, including the
subscription policy (on-change or periodic, with on-change in
general being the more challenging of the two), the period in which
to report changes (1 second periods will consume more resources than
1 hour periods), the amount of data in the subtree that is being
subscribed to, and the number and combination of other subscriptions
that are concurrently being serviced.</t>
<t>When providing access control to every node in a pushed update,
it is possible to make and update efficient access control filters
for an update. These filters can be set upon subscription and
applied against a stream of updates. These filters need only be
updated when (a) there is a new node added/removed from the
subscribed tree with different permissions than its parent, or (b)
read access permissions have been changed on nodes under the target
node for the subscriber.</t>
</section>
<section title="Alignment with RFC 5277bis">
<t>A new draft has been chartered by the Netconf Working Group to
replace the current Netconf Event Model defined in RFC 5277. Future
revisions of this document will leverage RFC 5277bis as applicable.
It is anticipated that portions of the data model and subscription
management that are now defined in this this document and that are
not applicable only to YANG-Push, but to more general event
subscriptions, will move to RFC 5277bis.</t>
</section>
</section>
</section>
<section title="A YANG data model for management of datastore push subscriptions">
<section title="Overview">
<t>The YANG data model for datastore push subscriptions is depicted in
the following figure.</t>
<figure align="center" anchor="model-structure"
title="Model structure">
<artwork align="left">
module: ietf-yang-push
augment /notif-bis:establish-subscription/notif-bis:input:
+---- subscription-start-time? yang:date-and-time
+---- subscription-stop-time? yang:date-and-time
+---- (update-trigger)?
| +--:(periodic)
| | +---- period yang:timeticks
| +--:(on-change) {on-change}?
| +---- no-synch-on-start? empty
| +---- dampening-period yang:timeticks
| +---- excluded-change* change-type
+---- dscp? inet:dscp
| {notif-bis:configured-subscriptions}?
+---- subscription-priority? uint8
+---- subscription-dependency? string
augment /notif-bis:establish-subscription/notif-bis:input/
| notif-bis:filter-type:
+--:(update-filter)
+---- (update-filter)?
+--:(subtree)
| +---- subtree-filter
+--:(xpath)
+---- xpath-filter? yang:xpath1.0
augment /notif-bis:establish-subscription/notif-bis:output:
+---- subscription-start-time? yang:date-and-time
+---- subscription-stop-time? yang:date-and-time
+---- (update-trigger)?
| +--:(periodic)
| | +---- period yang:timeticks
| +--:(on-change) {on-change}?
| +---- no-synch-on-start? empty
| +---- dampening-period yang:timeticks
| +---- excluded-change* change-type
+---- dscp? inet:dscp
| {notif-bis:configured-subscriptions}?
+---- subscription-priority? uint8
+---- subscription-dependency? string
augment /notif-bis:establish-subscription/notif-bis:output/
| notif-bis:result/notif-bis:no-success/notif-bis:filter-type:
+--:(update-filter)
+---- (update-filter)?
+--:(subtree)
| +---- subtree-filter
+--:(xpath)
+---- xpath-filter? yang:xpath1.0
augment /notif-bis:modify-subscription/notif-bis:input:
+---- subscription-start-time? yang:date-and-time
+---- subscription-stop-time? yang:date-and-time
+---- (update-trigger)?
| +--:(periodic)
| | +---- period yang:timeticks
| +--:(on-change) {on-change}?
| +---- no-synch-on-start? empty
| +---- dampening-period yang:timeticks
| +---- excluded-change* change-type
+---- dscp? inet:dscp
| {notif-bis:configured-subscriptions}?
+---- subscription-priority? uint8
+---- subscription-dependency? string
augment /notif-bis:modify-subscription/notif-bis:input/
| notif-bis:filter-type:
+--:(update-filter)
+---- (update-filter)?
+--:(subtree)
| +---- subtree-filter
+--:(xpath)
+---- xpath-filter? yang:xpath1.0
augment /notif-bis:modify-subscription/notif-bis:output:
+---- subscription-start-time? yang:date-and-time
+---- subscription-stop-time? yang:date-and-time
+---- (update-trigger)?
| +--:(periodic)
| | +---- period yang:timeticks
| +--:(on-change) {on-change}?
| +---- no-synch-on-start? empty
| +---- dampening-period yang:timeticks
| +---- excluded-change* change-type
+---- dscp? inet:dscp
| {notif-bis:configured-subscriptions}?
+---- subscription-priority? uint8
+---- subscription-dependency? string
augment /notif-bis:modify-subscription/notif-bis:output/
| notif-bis:result/notif-bis:no-success/notif-bis:filter-type:
+--:(update-filter)
+---- (update-filter)?
+--:(subtree)
| +---- subtree-filter
+--:(xpath)
+---- xpath-filter? yang:xpath1.0
augment /notif-bis:subscription-started:
+---- subscription-start-time? yang:date-and-time
+---- subscription-stop-time? yang:date-and-time
+---- (update-trigger)?
| +--:(periodic)
| | +---- period yang:timeticks
| +--:(on-change) {on-change}?
| +---- no-synch-on-start? empty
| +---- dampening-period yang:timeticks
| +---- excluded-change* change-type
+---- dscp? inet:dscp
| {notif-bis:configured-subscriptions}?
+---- subscription-priority? uint8
+---- subscription-dependency? string
augment /notif-bis:subscription-started/notif-bis:filter-type:
+--:(update-filter)
+---- (update-filter)?
+--:(subtree)
| +---- subtree-filter
+--:(xpath)
+---- xpath-filter? yang:xpath1.0
augment /notif-bis:subscription-modified:
+---- subscription-start-time? yang:date-and-time
+---- subscription-stop-time? yang:date-and-time
+---- (update-trigger)?
| +--:(periodic)
| | +---- period yang:timeticks
| +--:(on-change) {on-change}?
| +---- no-synch-on-start? empty
| +---- dampening-period yang:timeticks
| +---- excluded-change* change-type
+---- dscp? inet:dscp
| {notif-bis:configured-subscriptions}?
+---- subscription-priority? uint8
+---- subscription-dependency? string
augment /notif-bis:subscription-modified/notif-bis:filter-type:
+--:(update-filter)
+---- (update-filter)?
+--:(subtree)
| +---- subtree-filter
+--:(xpath)
+---- xpath-filter? yang:xpath1.0
augment /notif-bis:filters/notif-bis:filter/notif-bis:filter-type:
+--:(update-filter)
+--rw (update-filter)?
+--:(subtree)
| +--rw subtree-filter
+--:(xpath)
+--rw xpath-filter? yang:xpath1.0
augment /notif-bis:subscription-config/notif-bis:subscription:
+--rw subscription-start-time? yang:date-and-time
+--rw subscription-stop-time? yang:date-and-time
+--rw (update-trigger)?
| +--:(periodic)
| | +--rw period yang:timeticks
| +--:(on-change) {on-change}?
| +--rw no-synch-on-start? empty
| +--rw dampening-period yang:timeticks
| +--rw excluded-change* change-type
+--rw dscp? inet:dscp
| {notif-bis:configured-subscriptions}?
+--rw subscription-priority? uint8
+--rw subscription-dependency? string
augment /notif-bis:subscription-config/notif-bis:subscription/
| notif-bis:filter-type:
+--:(update-filter)
+--rw (update-filter)?
+--:(subtree)
| +--rw subtree-filter
+--:(xpath)
+--rw xpath-filter? yang:xpath1.0
augment /notif-bis:subscriptions/notif-bis:subscription:
+--ro subscription-start-time? yang:date-and-time
+--ro subscription-stop-time? yang:date-and-time
+--ro (update-trigger)?
| +--:(periodic)
| | +--ro period yang:timeticks
| +--:(on-change) {on-change}?
| +--ro no-synch-on-start? empty
| +--ro dampening-period yang:timeticks
| +--ro excluded-change* change-type
+--ro dscp? inet:dscp
| {notif-bis:configured-subscriptions}?
+--ro subscription-priority? uint8
+--ro subscription-dependency? string
augment /notif-bis:subscriptions/notif-bis:subscription/
| notif-bis:filter-type:
+--:(update-filter)
+--ro (update-filter)?
+--:(subtree)
| +--ro subtree-filter
+--:(xpath)
+--ro xpath-filter? yang:xpath1.0
notifications:
+---n push-update
| +--ro subscription-id notif-bis:subscription-id
| +--ro time-of-update? yang:date-and-time
| +--ro (encoding)?
| +--:(encode-xml)
| | +--ro datastore-contents-xml? datastore-contents-xml
| +--:(encode-json) {notif-bis:json}?
| +--ro datastore-contents-json? datastore-contents-json
+---n push-change-update {on-change}?
+--ro subscription-id notif-bis:subscription-id
+--ro time-of-update? yang:date-and-time
+--ro (encoding)?
+--:(encode-xml)
| +--ro datastore-changes-xml? datastore-changes-xml
+--:(encode-json) {notif-bis:json}?
+--ro datastore-changes-yang? datastore-changes-json
</artwork>
</figure>
<t>The components of the model are described in the following
subsections.</t>
</section>
<section title="Update streams">
<t>Container "update-streams" is used to indicate which data streams
are provided by the system and can be subscribed to. For this purpose,
it contains a leaf list of data nodes identifying the supported
streams.</t>
</section>
<section title="Filters">
<t>Container "filters" contains a list of configurable data filters,
each specified in its own list element. This allows users to configure
filters separately from an actual subscription, which can then be
referenced from a subscription. This facilitates the reuse of filter
definitions, which can be important in case of complex filter
conditions.</t>
<t>One of three types of filters can be specified as part of a filter
list element. Subtree filters follow syntax and semantics of RFC 6241
and allow to specify which subtree(s) to subscribe to. In addition,
XPath filters can be specified for more complex filter conditions.
Finally, filters can be specified using syntax and semantics of
RFC5277.</t>
<t>It is conceivable to introduce other types of filters; in that
case, the data model needs to be augmented accordingly.</t>
</section>
<section title="Subscription configuration">
<t>As an optional feature, configured-subscriptions, allows for the
configuration of subscriptions as opposed to RPC. Subscriptions
configurations are represented by list subscription-config. Each
subscription is represented through its own list element and includes
the following components: <list style="symbols">
<t>"subscription-id" is an identifier used to refer to the
subscription.</t>
<t>"stream" refers to the stream being subscribed to. The
subscription model assumes the presence of perpetual and
continuous streams of updates. Various streams are defined:
"push-update" covers the entire set of YANG data in the server.
"operational-push" covers all operational data, while
"config-push" covers all configuration data. Other streams could
be introduced in augmentations to the model by introducing
additional identities.</t>
<t>"encoding" refers to the encoding requested for the data
updates. By default, updates are encoded using XML. However, JSON
can be requested as an option if the json-enconding feature is
supported. Other encodings may be supported in the future.</t>
<t>"subscription-start-time" specifies when the subscription is
supposed to start. The start time also serves as anchor time for
periodic subscriptions (see below).</t>
<t>"subscription-stop-time" specifies a stop time for the
subscription. Once the stop time is reached, the subscription is
automatically terminated. However, even when terminated, the
subscription entry remains part of the configuration unless
explicity deleted from the configuration. It is possible to
effectively "resume" a stopped subscription by reconfiguring the
stop time.</t>
<t>Filters for a subscription can be specified using a choice,
allowing to either reference a filter that has been separately
configured or entering its definition inline.</t>
<t>A choice of subscription policies allows to define when to send
new updates - periodic or on change. <list style="symbols">
<t>For periodic subscriptions, the trigger is defined by a
"period", a parameter that defines the interval with which
updates are to be pushed. The start time of the subscription
serves as anchor time, defining one specific point in time at
which an update needs to be sent. Update intervals always fall
on the points in time that are a multiple of a period after
the start time.</t>
<t>For on-change subscriptions, the trigger occurs whenever a
change in the subscribed information is detected. On-change
subscriptions have more complex semantics that is guided by
additional parameters. "dampening-period" specifies the
interval that must pass before a successive update for the
same data node is sent. The first time a change is detected,
the update is sent immediately. If a subsequent change is
detected, another update is only sent once the dampening
period has passed, containing the value of the data node that
is then valid. "excluded-change" allows to restrict the types
of changes for which updates are sent (changes to object
values, object creation or deletion events).
"no-synch-on-start" is a flag that allows to specify whether
or not a complete update with all the subscribed data should
be sent at the beginning of a subscription; if the flag is
omitted, a complete update is sent to facilitate
synchronization. It is conceivable to augment the data model
with additional parameters in the future to specify even more
refined policies, such as parameters that specify the
magnitude of a change that must occur before an update is
triggered.</t>
</list></t>
<t>This is followed with a list of receivers for the subscription,
indicating for each receiver the transport that should be used for
push updates (if options other than Netconf are supported). It
should be noted that the receiver does not have to be the same
system that configures the subscription.</t>
<t>Finally, "push-source" can be used to specify the source of
push updates, either a specific interface or server address.</t>
</list> A subscription established through configuration cannot be
deleted using an RPC. Likewise, subscriptions established through RPC
cannot be deleted through configuration.</t>
<t>The deletion of a subscription, whether through RPC or
configuration, results in immediate termination of the
subsciption.</t>
</section>
<section title="Subscription monitoring">
<t>Subscriptions can be subjected to management themselves. For
example, it is possible that a server may no longer be able to serve a
subscription that it had previously accepted. Perhaps it has run out
of resources, or internal errors may have occurred. When this is the
case, a server needs to be able to temporarily suspend the
subscription, or even to terminate it. More generally, the server
should provide a means by which the status of subscriptions can be
monitored.</t>
<t>Container "subscriptions" contains the state of all subscriptions
that are currently active. This includes subscriptions that were
established (and have not yet been deleted) using RPCs, as well as
subscriptions that have been configured as part of configuration.</t>
<t>Each subscription is represented as a list element
"datastore-push-subscription". The associated information includes an
identifier for the subscription, a subscription status, as well as the
various subscription parameters that are in effect. The subscription
status indicates whether the subscription is currently active and
healthy, or if it is degraded in some form. Leaf
"configured-subscription" indicates whether the subscription came into
being via configuration or via RPC.</t>
<t>Subscriptions that were established by RPC are removed from the
list once they expire (reaching stop-time )or when they are
terminated. Subscriptions that were established by configuration need
to be deleted from the configuration by a configuration editing
operation.</t>
</section>
<section title="Notifications">
<t>A server needs to indicate any changes in status of a subscription
to the receiver through a notification. Specifically, subscribers need
to be informed of the following: <list style="symbols">
<t>A subscription has been temporarily suspended (including the
reason)</t>
<t>A subscription (that had been suspended earlier) is once again
operational</t>
<t>A subscription has been terminated (including the reason)</t>
<t>A subscription has been modified (including the current set of
subscription parameters in effect)</t>
</list> Finally, a server might provide additional information about
subscriptions, such as statistics about the number of data updates
that were sent. However, such information is currently outside the
scope of this specification.</t>
</section>
<section title="RPCs">
<t>YANG-Push subscriptions are established, modified, and deleted
using three RPCs.</t>
<section title="Establish-subscription RPC">
<t>The subscriber sends an establish-subscription RPC with the
parameters in section 3.1. For instance</t>
<figure align="center" anchor="establish-subscription-rpc"
title="Establish-subscription RPC">
<artwork align="left"><![CDATA[
<netconf:rpc message-id="101"
xmlns:netconf="urn:ietf:params:xml:ns:netconf:base:1.0">
<establish-subscription
xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-push:1.0">
<stream>push-update</stream>
<filter netconf:type="xpath"
xmlns:ex="http://example.com/sample-data/1.0"
select="/ex:foo"/>
<period>500</period>
<encoding>encode-xml</encoding>
</establish-subscription>
</netconf:rpc>
]]></artwork>
</figure>
<t>The server must respond explicitly positively (i.e., subscription
accepted) or negatively (i.e., subscription rejected) to the
request. Positive responses include the subscription-id of the
accepted subscription. In that case a server may respond:</t>
<figure align="center"
anchor="establish-subscription-positive-reply"
title="Establish-subscription positive RPC response">
<artwork align="left"><![CDATA[
<rpc-reply message-id="101"
xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
<subscription-result
xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-push:1.0">
ok
</subscription-result>
<subscription-id
xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-push:1.0">
52
</subscription-id>
</rpc-reply>
]]></artwork>
</figure>
<t>A subscription can be rejected for multiple reasons, including
the lack of authorization to establish a subscription, the lack of
read authorization on the requested data node, or the inability of
the server to provide a stream with the requested semantics. .</t>
<t>When the requester is not authorized to read the requested data
node, the returned <error-info> indicates an authorization
error and the requested node. For instance, if the above request was
unauthorized to read node "ex:foo" the server may return:</t>
<figure align="center"
anchor="establish-subscription-access-denied-reply"
title="Establish-subscription access denied response">
<artwork align="left"><![CDATA[
<rpc-reply message-id="101"
xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
<subscription-result
xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-push:1.0">
error-data-not-authorized
</subscription-result>
</rpc-reply>
]]></artwork>
</figure>
<t>If a request is rejected because the server is not able to serve
it, the server SHOULD include in the returned error what
subscription parameters would have been accepted for the request.
However, they are no guarantee that subsequent requests for this
client or others will in fact be accepted.</t>
<t>For example, for the following request:</t>
<figure align="center" anchor="establish-subscription-request-2"
title="Establish-subscription request example 2">
<artwork align="left"><![CDATA[
<netconf:rpc message-id="101"
xmlns:netconf="urn:ietf:params:xml:ns:netconf:base:1.0">
<establish-subscription
xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-push:1.0">
<stream>push-update</stream>
<filter netconf:type="xpath"
xmlns:ex="http://example.com/sample-data/1.0"
select="/ex:foo"/>
<dampening-period>10</dampening-period>
<encoding>encode-xml</encoding>
</establish-subscription>
</netconf:rpc>
]]></artwork>
</figure>
<t>A server that cannot serve on-change updates but periodic updates
might return the following:</t>
<figure align="center"
anchor="establish-subscription-error-response-2"
title="Establish-subscription error response example 2">
<artwork align="left"><![CDATA[
<rpc-reply message-id="101"
xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
<subscription-result
xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-push:1.0">
error-no-such-option
</subscription-result>
<period>100</period>
</rpc-reply>
]]></artwork>
</figure>
</section>
<section title="Modify-subscription RPC">
<t>The subscriber may send a modify-subscription PRC for a
subscription previously established using RPC The subscriber may
change any subscription parameters by including the new values in
the modify-subscription RPC. Parameters not included in the rpc
should remain unmodified. For illustration purposes we include an
exchange example where a subscriber modifies the period of the
subscription.</t>
<figure align="center" anchor="modify-subscription-request"
title="Modify subscription request">
<artwork align="left"><![CDATA[
<netconf:rpc message-id="102"
xmlns:netconf="urn:ietf:params:xml:ns:netconf:base:1.0">
<modify-subscription
xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-push:1.0">
<stream>push-update</stream>
<subscription-id>
1011
</subscription-id>
<filter netconf:type="xpath"
xmlns:ex="http://example.com/sample-data/1.0"
select="/ex:foo"/>
<period>250</period>
<encoding>encode-xml</encoding>
</modify-subscription>
</netconf:rpc>
]]></artwork>
</figure>
<t>The server must respond explicitly positively (i.e., subscription
accepted) or negatively (i.e., subscription rejected) to the
request. Positive responses include the subscription-id of the
accepted subscription. In that case a server may respond:</t>
<figure align="center" anchor="modify-subscription-response"
title="Modify subscription response">
<artwork align="left"><![CDATA[
<rpc-reply message-id="102"
xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
<subscription-result
xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-push:1.0">
ok
</subscription-result>
<subscription-id
xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-push:1.0">
1011
</subscription-id>
</rpc-reply>
]]></artwork>
</figure>
<t>If the subscription modification is rejected, the server must
send a response like it does for an establish-subscription and
maintain the subscription as it was before the modification request.
A subscription may be modified multiple times.</t>
<t>A configured subscription cannot be modified using
modify-subscription RPC. Instead, the configuration needs to be
edited as needed.</t>
</section>
<section title="Delete-subscription RPC">
<t>To stop receiving updates from a subscription and effectively
delete a subscription that had previously been established using an
establish-subscription RPC, a subscriber can send a
delete-subscription RPC, which takes as only input the
subscription-id. For example</t>
<figure align="center" anchor="delete-subscription"
title="Delete subscription">
<artwork align="left"><![CDATA[
<netconf:rpc message-id="103"
xmlns:netconf="urn:ietf:params:xml:ns:netconf:base:1.0">
<delete-subscription
xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-push:1.0">
<subscription-id>
1011
</subscription-id>
</delete-subscription>
</netconf:rpc>
<rpc-reply message-id="103"
xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
<ok/>
</rpc-reply>
]]></artwork>
</figure>
<t>Configured subscriptions cannot be deleted via RPC, but have to
be removed from the configuration.</t>
</section>
</section>
</section>
<section anchor="YANG-module" title="YANG module">
<t><figure>
<artwork><![CDATA[
<CODE BEGINS> file "ietf-yang-push@2016-06-15.yang"
module ietf-yang-push {
namespace "urn:ietf:params:xml:ns:yang:ietf-yang-push";
prefix yp;
import ietf-inet-types {
prefix inet;
}
import ietf-yang-types {
prefix yang;
}
import ietf-event-notifications {
prefix notif-bis;
}
import ietf-5277-netconf {
prefix notif;
}
organization "IETF";
contact
"WG Web: <http://tools.ietf.org/wg/netconf/>
WG List: <mailto:netconf@ietf.org>
WG Chair: Mahesh Jethanandani
<mailto:mjethanandani@gmail.com>
WG Chair: Mehmet Ersue
<mailto:mehmet.ersue@nokia.com>
Editor: Alexander Clemm
<mailto:alex@cisco.com>
Editor: Eric Voit
<mailto:evoit@cisco.com>
Editor: Alberto Gonzalez Prieto
<mailto:albertgo@cisco.com>
Editor: Ambika Prasad Tripathy
<mailto:ambtripa@cisco.com>
Editor: Einar Nilsen-Nygaard
<mailto:einarnn@cisco.com>";
description
"This module contains conceptual YANG specifications
for YANG push.";
revision 2016-06-15 {
description
"First revision to incorporate RFC 5277-bis.";
reference "YANG Datastore Push, draft-ietf-netconf-yang-push-03";
}
feature on-change {
description
"This feature indicates that on-change updates are
supported.";
}
/*
* IDENTITIES
*/
/* Additional errors for subscription operations */
identity error-data-not-authorized {
base notif-bis:error;
description
"No read authorization for a requested data node.";
}
/* Additional types of streams */
identity update-stream {
base notif:stream;
description
"Base identity to represent a conceptual system-provided
datastream of datastore updates with predefined semantics.";
}
identity yang-push {
base update-stream;
description
"A conceptual datastream consisting of all datastore
updates, including operational and configuration data.";
}
identity operational-push {
base update-stream;
description
"A conceptual datastream consisting of updates of all
operational data.";
}
identity config-push {
base update-stream;
description
"A conceptual datastream consisting of updates of all
configuration data.";
}
identity custom-stream {
base update-stream;
description
"A conceptual datastream for datastore
updates with custom updates as defined by a user.";
}
/* Additional transport option */
identity restconf {
base notif-bis:transport;
description
"Restconf notifications as a transport";
}
/*
* TYPE DEFINITIONS
*/
typedef datastore-contents-xml {
type string;
description
"This type is be used to represent datastore contents,
i.e. a set of data nodes with their values, in XML.
The syntax corresponds to the syntax of the data payload
returned in a corresponding Netconf get operation with the
same filter parameters applied.";
reference "RFC 6241 section 7.7";
}
typedef datastore-changes-xml {
type string;
description
"This type is used to represent a set of changes in a
datastore encoded in XML, indicating for datanodes whether
they have been created, deleted, or updated. The syntax
corresponds to the syntax used to when editing a
datastore using the edit-config operation in Netconf.";
reference "RFC 6241 section 7.2";
}
typedef datastore-contents-json {
type string;
description
"This type is be used to represent datastore contents,
i.e. a set of data nodes with their values, in JSON.
The syntax corresponds to the syntax of the data
payload returned in a corresponding RESTCONF get
operation with the same filter parameters applied.";
reference "RESTCONF Protocol";
}
typedef datastore-changes-json {
type string;
description
"This type is used to represent a set of changes in a
datastore encoded in JSON, indicating for datanodes whether
they have been created, deleted, or updated. The syntax
corresponds to the syntax used to patch a datastore
using the yang-patch operation with Restconf.";
reference "draft-ietf-netconf-yang-patch";
}
typedef filter-id {
type uint32;
description
"A type to identify filters which can be associated with a
subscription.";
}
typedef subscription-result {
type identityref {
base notif-bis:subscription-result;
}
description
"The result of a subscription operation";
}
typedef subscription-term-reason {
type identityref {
base notif-bis:subscription-errors;
}
description
"Reason for a server to terminate a subscription.";
}
typedef subscription-susp-reason {
type identityref {
base notif-bis:subscription-errors;
}
description
"Reason for a server to suspend a subscription.";
}
typedef encoding {
type identityref {
base notif-bis:encodings;
}
description
"Specifies a data encoding, e.g. for a data subscription.";
}
typedef change-type {
type enumeration {
enum "create" {
description
"A new data node was created";
}
enum "delete" {
description
"A data node was deleted";
}
enum "modify" {
description
"The value of a data node has changed";
}
}
description
"Specifies different types of changes that may occur
to a datastore.";
}
typedef transport-protocol {
type identityref {
base notif-bis:transport;
}
description
"Specifies transport protocol used to send updates to a
receiver.";
}
typedef push-source {
type enumeration {
enum "interface-originated" {
description
"Pushes will be sent from a specific interface on a
Publisher";
}
enum "address-originated" {
description
"Pushes will be sent from a specific address on a
Publisher";
}
}
description
"Specifies from where objects will be sourced when being pushed
off a publisher.";
}
typedef update-stream {
type identityref {
base update-stream;
}
description
"Specifies a system-provided datastream.";
}
grouping update-filter {
description
"This groupings defines filters for push updates for a datastore
tree. The filters define which updates are of interest in a
push update subscription.
Mixing and matching of multiple filters does not occur
at the level of this grouping.
When a push-update subscription is created, the filter can
be a regular subscription filter, or one of the additional
filters that are defined in this grouping.";
choice update-filter {
description
"Define filters regarding which data nodes to include
in push updates";
case subtree {
description
"Subtree filter.";
anyxml subtree-filter {
description
"Subtree-filter used to specify the data nodes targeted
for subscription within a subtree, or subtrees, of a
conceptual YANG datastore.
It may include additional criteria,
allowing users to receive only updates of a limited
set of data nodes that match those filter criteria.
This will be used to define what
updates to include in a stream of update events, i.e.
to specify for which data nodes update events should be
generated and specific match expressions that objects
need to meet. The syntax follows the subtree filter
syntax specified in RFC 6241, section 6.";
reference "RFC 6241 section 6";
}
}
case xpath {
description
"XPath filter";
leaf xpath-filter {
type yang:xpath1.0;
description
"Xpath defining the data items of interest.";
}
}
}
}
grouping update-policy {
description
"This grouping describes the conditions under which an
update will be sent as part of an update stream.";
choice update-trigger {
description
"Defines necessary conditions for sending an event to
the subscriber.";
case periodic {
description
"The agent is requested to notify periodically the
current values of the datastore or the subset
defined by the filter.";
leaf period {
type yang:timeticks;
mandatory true;
description
"Duraton of time which should occur between periodic
push updates. Where the anchor of a start-time is
available, the push will include the objects and their
values which exist at an exact multiple of timeticks
aligning to this start-time anchor.";
}
}
case on-change {
if-feature "on-change";
description
"The agent is requested to notify changes in
values in the datastore or a subset of it defined
by a filter.";
leaf no-synch-on-start {
type empty;
description
"This leaf acts as a flag that determines behavior at the
start of the subscription. When present,
synchronization of state at the beginning of the
subscription is outside the scope of the subscription.
Only updates about changes that are observed from the
start time, i.e. only push-change-update notifications
are sent.
When absent (default behavior), in order to facilitate
a receiver's synchronization, a full update is sent
when the subscription starts using a push-update
notification, just like in the case of a periodic
subscription. After that, push-change-update
notifications are sent.";
}
leaf dampening-period {
type yang:timeticks;
mandatory true;
description
"Minimum amount of time that needs to have
passed since the last time an update was
provided.";
}
leaf-list excluded-change {
type change-type;
description
"Use to restrict which changes trigger an update.
For example, if modify is excluded, only creation and
deletion of objects is reported.";
}
}
}
}
grouping push-subscription-info {
description
"This grouping describes information concerning a
push subscription that is need in addition to information
already included in notif-bis:subscription-info.";
leaf subscription-start-time {
type yang:date-and-time;
description
"Designates the time at which a subscription is supposed
to start, or immediately, in case the start-time is in
the past. For periodic subscription, the start time also
serves as anchor time from which the time of the next
update is computed. The next update will take place at the
next period interval from the anchor time.
For example, for an anchor time at the top of a minute
and a period interval of a minute, the next update will
be sent at the top of the next minute.";
}
leaf subscription-stop-time {
type yang:date-and-time;
description
"Designates the time at which a subscription will end.
When a subscription reaches its stop time, it will be
automatically deleted. No final push is required unless there
is exact alignment with the end of a periodic subscription
period.";
}
}
grouping subscription-qos {
description
"This grouping describes Quality of Service information
concerning a subscription. This information is passed to lower
layers for transport priortization and treatment";
leaf dscp {
if-feature "notif-bis:configured-subscriptions";
type inet:dscp;
default "0";
description
"The push update's IP packet transport priority.
This is made visible across network hops to receiver.
The transport priority is shared for all receivers of
a given subscription.";
}
leaf subscription-priority {
type uint8;
description
"Relative priority for a subscription. Allows an underlying
transport layer perform informed load balance allocations
between various subscriptions";
}
leaf subscription-dependency {
type string;
description
"Provides the Subscription ID of a parent subscription
without which this subscription should not exist. In
other words, there is no reason to stream these objects
if another subscription is missing.";
}
}
augment "/notif-bis:establish-subscription/notif-bis:input" {
description
"Define additional subscription parameters that apply
specifically to push updates";
uses push-subscription-info;
uses update-policy;
uses subscription-qos;
}
augment "/notif-bis:establish-subscription/notif-bis:input/notif-bis:filter-type" {
description
"Add push filters to selection of filter types.";
case update-filter {
description
"Additional filter options for push subscription.";
uses update-filter;
}
}
augment "/notif-bis:establish-subscription/notif-bis:output" {
description
"Allow to return additional subscription parameters that apply
specifically to push updates.";
uses push-subscription-info;
uses update-policy;
uses subscription-qos;
}
augment "/notif-bis:establish-subscription/notif-bis:output/"+
"notif-bis:result/notif-bis:no-success/notif-bis:filter-type" {
description
"Add push filters to selection of filter types.";
case update-filter {
description
"Additional filter options for push subscription.";
uses update-filter;
}
}
augment "/notif-bis:modify-subscription/notif-bis:input" {
description
"Define additional subscription parameters that apply
specifically to push updates.";
uses push-subscription-info;
uses update-policy;
uses subscription-qos;
}
augment "/notif-bis:modify-subscription/notif-bis:input/notif-bis:filter-type" {
description
"Add push filters to selection of filter types.";
case update-filter {
description
"Additional filter options for push subscription.";
uses update-filter;
}
}
augment "/notif-bis:modify-subscription/notif-bis:output" {
description
"Allow to retun additional subscription parameters that apply
specifically to push updates.";
uses push-subscription-info;
uses update-policy;
uses subscription-qos;
}
augment "/notif-bis:modify-subscription/notif-bis:output/"+
"notif-bis:result/notif-bis:no-success/notif-bis:filter-type" {
description
"Add push filters to selection of filter types.";
case update-filter {
description
"Additional filter options for push subscription.";
uses update-filter;
}
}
notification push-update {
description
"This notification contains a periodic push update.
This notification shall only be sent to receivers
of a subscription; it does not constitute a general-purpose
notification.";
leaf subscription-id {
type notif-bis:subscription-id;
mandatory true;
description
"This references the subscription because of which the
notification is sent.";
}
leaf time-of-update {
type yang:date-and-time;
description
"This leaf contains the time of the update.";
}
choice encoding {
description
"Distinguish between the proper encoding that was specified
for the subscription";
case encode-xml {
description
"XML encoding";
leaf datastore-contents-xml {
type datastore-contents-xml;
description
"This contains data encoded in XML,
per the subscription.";
}
}
case encode-json {
if-feature "notif-bis:json";
description
"JSON encoding";
leaf datastore-contents-json {
type datastore-contents-json;
description
"This leaf contains data encoded in JSON,
per the subscription.";
}
}
}
}
notification push-change-update {
if-feature "on-change";
description
"This notification contains an on-change push update.
This notification shall only be sent to the receivers
of a subscription; it does not constitute a general-purpose
notification.";
leaf subscription-id {
type notif-bis:subscription-id;
mandatory true;
description
"This references the subscription because of which the
notification is sent.";
}
leaf time-of-update {
type yang:date-and-time;
description
"This leaf contains the time of the update, i.e. the
time at which the change was observed.";
}
choice encoding {
description
"Distinguish between the proper encoding that was specified
for the subscription";
case encode-xml {
description
"XML encoding";
leaf datastore-changes-xml {
type datastore-changes-xml;
description
"This contains datastore contents that has changed
since the previous update, per the terms of the
subscription. Changes are encoded analogous to
the syntax of a corresponding Netconf edit-config
operation.";
}
}
case encode-json {
if-feature "notif-bis:json";
description
"JSON encoding";
leaf datastore-changes-yang {
type datastore-changes-json;
description
"This contains datastore contents that has changed
since the previous update, per the terms of the
subscription. Changes are encoded analogous
to the syntax of a corresponding RESTCONF yang-patch
operation.";
}
}
}
}
augment "/notif-bis:subscription-started" {
description
"This augmentation adds push subscription parameters
to the notification that a subscription has
started and data updates are beginning to be sent.
This notification shall only be sent to receivers
of a subscription; it does not constitute a general-purpose
notification.";
uses push-subscription-info;
uses update-policy;
uses subscription-qos;
}
augment "/notif-bis:subscription-started/notif-bis:filter-type" {
description
"This augmentation allows to include additional update filters
options to be included as part of the notification that a
subscription has started.";
case update-filter {
description
"Additional filter options for push subscription.";
uses update-filter;
}
}
augment "/notif-bis:subscription-modified" {
description
"This augmentation adds push subscription parameters
to the notification that a subscription has
been modified.
This notification shall only be sent to receivers
of a subscription; it does not constitute a general-purpose
notification.";
uses push-subscription-info;
uses update-policy;
uses subscription-qos;
}
augment "/notif-bis:subscription-modified/notif-bis:filter-type" {
description
"This augmentation allows to include additional update filters
options to be included as part of the notification that a
subscription has been modified.";
case update-filter {
description
"Additional filter options for push subscription.";
uses update-filter;
}
}
augment "/notif-bis:filters/notif-bis:filter/notif-bis:filter-type" {
description
"This container adds additional update filter options
to the list of configurable filters
that can be applied to subscriptions. This facilitates
the reuse of complex filters once defined.";
case update-filter {
uses update-filter;
}
}
augment "/notif-bis:subscription-config/notif-bis:subscription" {
description
"Contains the list of subscriptions that are configured,
as opposed to established via RPC or other means.";
uses push-subscription-info;
uses update-policy;
uses subscription-qos;
}
augment "/notif-bis:subscription-config/notif-bis:subscription/notif-bis:filter-type" {
description
"Add push filters to selection of filter types.";
case update-filter {
uses update-filter;
}
}
augment "/notif-bis:subscriptions/notif-bis:subscription" {
description
"Contains the list of currently active subscriptions,
i.e. subscriptions that are currently in effect,
used for subscription management and monitoring purposes.
This includes subscriptions that have been setup via RPC
primitives, e.g. establish-subscription, delete-subscription,
and modify-subscription, as well as subscriptions that
have been established via configuration.";
uses push-subscription-info;
uses update-policy;
uses subscription-qos;
}
augment "/notif-bis:subscriptions/notif-bis:subscription/notif-bis:filter-type" {
description
"Add push filters to selection of filter types.";
case update-filter {
description
"Additional filter options for push subscription.";
uses update-filter;
}
}
}
<CODE ENDS>
]]></artwork>
</figure></t>
</section>
<section title="Security Considerations">
<t>Subscriptions could be used to attempt to overload servers of YANG
datastores. For this reason, it is important that the server has the
ability to decline a subscription request if it would deplete its
resources. In addition, a server needs to be able to suspend an existing
subscription when needed. When this occur, the subscription status is
updated accordingly and the clients are notified. Likewise, requests for
subscriptions need to be properly authorized.</t>
<t>A subscription could be used to retrieve data in subtrees that a
client has not authorized access to. Therefore it is important that data
pushed based on subscriptions is authorized in the same way that regular
data retrieval operations are. Data being pushed to a client needs
therefore to be filtered accordingly, just like if the data were being
retrieved on-demand. The Netconf Authorization Control Model
applies.</t>
<t>A subscription could be configured on another receiver's behalf, with
the goal of flooding that receiver with updates. One or more publishers
could be used to overwhelm a receiver which doesn't even support
subscriptions. Clients which do not want pushed data need only terminate
or refuse any transport sessions from the publisher. In addition, the
Netconf Authorization Control Model SHOULD be used to control and
restrict authorization of subscription configuration.</t>
</section>
<section title="Issues that are currently being worked and resolved">
<section title="Unresolved issues under discussion">
<t>
<list style="symbols">
<t>Which stream types to introduce. Current list includes streams for all operational and for all
config data. Consider adding stream for operational data minus counters.
Also: assess implications of opstate implications on required data streams. </t>
<t>In addition to identifying which items go to which streams,
identifying and calling out which items (such as counters)
should not be "on-change subscribable" may be useful.
Consider introducing a Yang extension to define if an object:
is-a-counter and/or not-notifiable.</t>
<t>What QoS parameters should be supported for subscriptions.
Note: QoS parameters are applicable to buffering as well as temporarily loss of transport connectivity. </t>
<t>Implications of ephemeral requirements from I2RS</t>
<t>Filters: YANG 1.1 allows filters to be defined in multiple places.
How do they intersect each other in a deterministic way.</t>
<t>On-change subscription: consider providing publisher with capability to
initiate a refresh of contents rather than send deltas. Current proposal
allows for a "synch-on-start" option; such an option might be useful
also e.g. on resumption of a subscription that had been suspended.</t>
<t>Do we need an extension for NACM to support filter out datastore nodes
for which the receiver has no read access?
(And how does this differ from existing GET, which must do the same filtering?)
In 5277, such filtering is done at the notification level.
Yang-push includes notification-content filtering.
This may be very expensive in terms of processing.
Andy suggestion: only accept Yang-push subscriptions for subtrees
the user has rights for all the nodes in the subtree.
Changes to those rights trigger a subscription termination.
Should we codify this, or let vendors determine when per
subtree filtering might be applied?</t>
</list>
</t>
</section>
<section title="Agreement in principal">
<t>Still need to agree on draft text
<list style="symbols">
<t>Multiple receivers per configured subscription is ok.</t>
<t>Proper behavior for on-change, including detecting and indicating changes within a dampening period.</t>
<t>Still some details to work through, e.g.,
do we add a counter for the number of object changes during a dampening period?</t>
<t>Negotiate vs. auto-adjust. Cases where negotiate is needed exists for domain synchronization.
Error messages can be used to transport information back as hints.
Alternative is dedicated RPC responses.
In either case specific contents of these negotiation messages must still be defined.</t>
<t>Message format for synchronization (i.e. synch-on-start) still needs to be defined.</t>
</list>
</t>
</section>
<section title="Closed Issues">
<t>Some editorial updates needed to reflect these
<list style="symbols">
<t>Periodic interval goes to seconds from timeticks</t>
<t>Balancing Augment vs. Parallel Model structures (maximize augment)</t>
<t>Moving from separate start/stop to Anchor time for Periodic</t>
</list></t>
</section>
</section>
<section title="Acknowledgments">
<t>For their valuable comments, discussions, and feedback, we wish to acknowledge Andy Bierman, Yang Geng, Peipei Guo, Susan Hares, Tim Jenkins, Balazs Lengyel, Kent Watsen, and Guangying Zheng.
</t>
</section>
</middle>
<back>
<references title="Normative References">
&RFC1157;
<reference anchor="RFC5277">
<front>
<title>NETCONF Event Notifications</title>
<author fullname="Sharon Chisholm" initials="S" surname="Chisholm">
<organization/>
</author>
<author fullname="Hector Trevino" initials="H" surname="Trevino">
<organization/>
</author>
<date month="July" year="2008"/>
</front>
<seriesInfo name="RFC" value="5277"/>
</reference>
&RFC6020;
&RFC6241;
<reference anchor="RFC6470">
<front>
<title>Network Configuration Protocol (NETCONF) Base
Notifications</title>
<author fullname="Andy Bierman" initials="A" surname="Bierman">
<organization/>
</author>
<date month="February" year="2012"/>
</front>
<seriesInfo name="RFC" value="5277"/>
</reference>
&RFC6536;
</references>
<references title="Informative References">
<reference anchor="I-D.ietf-netconf-restconf">
<front>
<title>RESTCONF Protocol</title>
<author fullname="A. Bierman" initials="A." surname="Bierman">
<organization/>
</author>
<author fullname="M. Bjorklund" initials="M." surname="Bjorklund">
<organization/>
</author>
<author fullname="K. Watsen" initials="K." surname="Watsen">
<organization/>
</author>
<date day="27" month="April" year="2016"/>
</front>
<seriesInfo name="I-D" value="draft-ietf-netconf-restconf-13"/>
</reference>
<reference anchor="I-D.ietf-netconf-yang-patch">
<front>
<title>YANG Patch Media Type</title>
<author fullname="Andy Bierman" initials="A" surname="Bierman">
<organization/>
</author>
<author fullname="Martin Bjorklund" initials="M" surname="Bjorklund">
<organization/>
</author>
<author fullname="Kent Watsen" initials="K" surname="Watsen">
<organization/>
</author>
<date day="16" month="March" year="2016"/>
</front>
<seriesInfo name="Internet-Draft"
value="draft-ietf-netconf-yang-patch-08"/>
<format target="http://www.ietf.org/internet-drafts/draft-ietf-netconf-yang-patch-08.txt"
type="TXT"/>
</reference>
<reference anchor="I-D.i2rs-pub-sub-requirements">
<front>
<title>Requirements for Subscription to YANG Datastores</title>
<author fullname="Eric Voit" initials="E" surname="Voit">
<organization/>
</author>
<author fullname="Alexander Clemm" initials="A" surname="Clemm">
<organization/>
</author>
<author fullname="Alberto Gonzalez Prieto" initials="A"
surname="Gonzalez Prieto">
<organization/>
</author>
<date day="18" month="May" year="2016"/>
</front>
<seriesInfo name="Internet-Draft"
value="draft-ietf-i2rs-pub-sub-requirements-09"/>
<format target="http://www.ietf.org/internet-drafts/draft-ietf-i2rs-pub-sub-requirements-09.txt"
type="TXT"/>
</reference>
<reference anchor="I-D.voit-netmod-yang-mount-requirements">
<front>
<title>Requirements for Peer Mounting of YANG subtrees from Remote
Datastores</title>
<author fullname="Eric Voit" initials="E" surname="Voit">
<organization/>
</author>
<author fullname="Alexander Clemm" initials="A" surname="Clemm">
<organization/>
</author>
<author fullname="Sander Mertens" initials="S" surname="Mertens">
<organization/>
</author>
<date day="18" month="March" year="2016"/>
</front>
<seriesInfo name="Internet-Draft"
value="draft-voit-netmod-yang-mount-requirements-00"/>
<format target="http://www.ietf.org/internet-drafts/draft-voit-netmod-yang-mount-requirements-00.txt"
type="TXT"/>
</reference>
<reference anchor="I-D.clemm-netmod-mount">
<front>
<title>Mounting YANG-defined information from remote
datastores</title>
<author fullname="Alexander Clemm" initials="A" surname="Clemm">
<organization/>
</author>
<author fullname="Jan Medved" initials="J" surname="Medved">
<organization/>
</author>
<author fullname="Eric Voit" initials="E" surname="Voit">
<organization/>
</author>
<date day="21" month="March" year="2016"/>
</front>
<seriesInfo name="Internet-Draft" value="draft-clemm-netmod-mount-04"/>
<format target="http://www.ietf.org/internet-drafts/draft-clemm-netmod-mount-04.txt"
type="TXT"/>
</reference>
<reference anchor="I-D.ietf-netmod-yang-json">
<front>
<title>JSON Encoding of Data Modeled with YANG</title>
<author fullname="Ladislav Lhotka" initials="L" surname="Lhotka">
<organization/>
</author>
<date day="26" month="March" year="2016"/>
</front>
<seriesInfo name="Internet-Draft"
value="draft-ietf-netmod-yang-json-10"/>
<format target="http://www.ietf.org/internet-drafts/draft-ietf-netmod-yang-json-10.txt"
type="TXT"/>
</reference>
<reference anchor="I-D.gonzalez-netconf-5277bis">
<front>
<title>Subscribing to YANG-Defined Event Notifications</title>
<author fullname="Alberto Gonzalez Prieto" initials="A"
surname="Gonzalez Prieto">
<organization/>
</author>
<author fullname="Alexander Clemm" initials="A" surname="Clemm">
<organization/>
</author>
<author fullname="Eric Voit" initials="E" surname="Voit">
<organization/>
</author>
<author fullname="Ambika Prasad Tripathy" initials="A"
surname="Tripathy">
<organization/>
</author>
<author fullname="Einar Nilsen-Nygaard" initials="E"
surname="Nilsen-Nygaard">
<organization/>
</author>
<author fullname="Sharon Chisholm" initials="S"
surname="Chisholm">
<organization/>
</author>
<author fullname="Hector Trevino" initials="H"
surname="Trevino">
<organization/>
</author>
<date day="15" month="June" year="2016"/>
</front>
<seriesInfo name="Internet-Draft" value="draft-clemm-netmod-mount-03"/>
<format target="http://www.ietf.org/internet-drafts/draft-clemm-netmod-mount-03.txt"
type="TXT"/>
</reference>
<!--
&I-D.ietf-netmod-interfaces-cfg;
-->
</references>
</back>
</rfc>
| PAFTECH AB 2003-2026 | 2026-04-23 14:27:49 |